The purpose of the proposed study is to investigate the genetic contribution to impulsive aggressive behavior in patients with personality disorders, utilizing known polymorphisms in serotonin-related genes. Impulsive aggressive behavior is prevalent in patients with personality disorders and accounts for a substantial portion of the morbidity associated with these disorders. It is logical to investigate the association between genotype in serotonin-related genes and impulsive aggression in patients with personality disorders, in light of the observations that: 1) decreased serotonergic activity in the central nervous system has been demonstrated in personality disordered patients with impulsive aggressive behavior; 2) impulsive aggression has been shown to be at least partially heritable; 3) serotonin-related polymorphisms (variability in genotype) have been described, allowing for the characterization of genotype in individual subjects; In addition, we propose to measure central serotonin function utilizing the prolactin response to fenfluramine to allow for comparisons with both genotype and clinical phenomena.